Posters

Drainage basins, or catchments, are a common geomorphological feature on Earth, defined as an area where water from precipitation or other sources collects and drains. Using the morphological parameter of the circularity function developed by Stepinski and Stepinski (2005), one can model how a basin’s elongation shifts with elevation; this is a shape parameter previously demonstrated to correlate with the climate where basins form. In this study, the circularity function is used to analyze small basaltic, alluvial catchments primarily found in periglacial environments on Earth. Such basins may bear similarities to what appear to be alluvial catchments on Martian crater walls. This similarity makes attempts to draw connections between terrestrial catchment morphology and their climate of formation lucrative for probing the Mars climate debate. In order to analyze basin morphology, hierarchical clustering, a technique that groups vectors into a tree based on their similarity, is used to perform unsupervised classification of basins based solely on circularity function. Ultimately, clusters determined by the hierarchical clustering did not consistently correlate with climate parameters of annual precipitation or temperature. Further investigation into supervised learning techniques for classification is underway, as well as a deeper examination of the limitations of the circularity function as a classifier given available datasets.

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Turbulence is an important factor in protoplanetary disk evolution and the planet forma- tion process, but observational constraints are still limited. We addressed two obstacles in understanding the demographics of turbulence in protoplanetary disks. Firstly, the sample of protoplanetary disks for which turbulence has been estimated is small and not representative of the entire population. We identified candidate protoplanetary disks with high signal-to-noise ratio archival ALMA molecular line observations that explore unsampled regions of the stellar mass, disk mass, and accretion rate distributions of the disk population, and archival ALMA data for one of these objects, Sz 91, was processed and prepared for modelling. Secondly, in earlier work attempting to fit a double disk model to the warped disk around HD 100546, the Markov Chain Monte Carlo method used – EMCEE with the default stretch move – didn’t accurately converge to the global maximum of the posterior distribution. Alternative methods for sampling the posterior distribution – MultiNest and EMCEE with different moves – were explored and tested on a variety of test data sets, each generated from a pair of Gaussians. MultiNest successfully converged to the true parameter values for data generated with a range of parameters and signal-to-noise ratios, while EMCEE had more uneven performance. EMCEE performed best with differential evolution (DE) snooker move, mixtures of DE snooker move and DE move, and stretch move, but there were some data sets for which EMCEE failed. Notably, EMCEE with stretch move failed to converge in a test scenario where the Gaussians were seperated by a large gap, which resulted in a multi-modal posterior distribution. Since we think this is a similar reason to why EMCEE with stretch move didn’t accurately converge with HD 100546, this result suggests that an alternative Monte Carlo method might allow for successful modelling of that disk. Future work will test these methods on real ALMA data from a previously modelled protoplanetary disk.

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To further understand the molecular content of planetary nebulae (PNe), we use the Sub- millimeter Telescope (SMT) on Mt. Graham and 12-m Telescope at Kitt Peak, both facilities of the Arizona Radio Observatory, to observe the J=3-2 and J=1-0 transitions of molecules HCN and HCO+ in thirteen sources. The sources vary in age, morphology, distance, and size as detailed in Table 1 and have been chosen because CO has previously been detected in them Schmidt & Ziurys (2016). The survey of these PNe has been a success, with HCN being identified in at least one transition in ten sources and HCO+ in eleven. More data is required to finish this work as a result of the closure of the telescopes this year; however with available measurements, the detection rate for HCN and HCO+ is 81%, which is consistent with the findings of Schmidt & Ziurys (2016) that polyatomic molecules are common in PNe. Furthermore, our results indicate stable molecular abundances over time in contrast to previous models such as that of Redman et al. (2003) which predict rapid depletion of molecular content in PNe.

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White dwarfs are the end state of all low mass stars, including our sun. Theory suggests that some planets should be able to survive their host star’s transition, however there have only been two detected planet transits around white dwarfs. Using data from Sectors 1-25 of the Transiting Exoplanet Survey Satellite (TESS), we searched 1411 targets for exoplanets orbiting white dwarfs at a period less than 2.31 days. There were 4 white dwarfs that showed promising variability indicating a possible exoplanet transit when initially analyzed: TIC 194303300 observed in Sector 17, TIC 453828065 observed in Sector 4, TIC 333527240 observed in Sector 19, and TIC 394131772 observed in Sectors 14, 15, and 16. However, upon further evaluation, we show that background eclipsing binaries are the likely source of variability, so we have not confirmed any new planets around white dwarfs in the TESS data. This project was supported in part by the NSF REU grant AST-1757321 and by the Nantucket Maria Mitchell Association.

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While wide binaries (>100 AU) appear to be very similar to single stars in their disk mass distribution, sub-mm observations show medium binaries (15-100 AU) to have a destructive influence on their proto-planetary disk material. The occurrence rate of planets around tight binaries (<15 AU) and single stars, however, is similar, and distinctly larger than around medium binaries. We take sub-mm observations of 129 known tight binaries in Orion A, building on the sparse statistics around these systems. We compare our measured disk mass distribution to those of single stars and medium binaries. Our analysis has only found a significant difference between tight binaries and medium binaries.

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Debris disks are tenuous, dusty belts surrounding main sequence stars generated by collisions between planetesimals. HD 206893 is one of only two stars known to host a directly imaged brown dwarf orbiting interior to its debris ring, in this case at a projected separation of 10.4 au. Here we resolve structure in the debris disk around HD 206893 at an angular resolution of 0′.′6 (24 au) and wavelength of 1.3 mm with the Atacama Large Millimeter/submillimeter Array (ALMA). We observe a broad disk extending from a radius of < 34 au to 158+6-6au. We model the disk with a continuous, gapped, and double power-law model of the surface density profile, and find strong evidence for a local minimum in the surface density distribution near a radius of 70 au, likely due to a gap in the disk with an inner radius of 73+5-9 au and width 13+5-7 au. Gapped structure has been observed in four other debris disks – essentially every other debris disk observed with sufficient angular resolution and sensitivity with ALMA – and would be suggestive of an additional planetary-mass companion.

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Within the stellar winds of O stars, small pockets of gas are shock heated to x-ray emitting temperatures. We can use emission line complexes in the x-ray spectrum, composed of forbidden, intercombination, and resonance lines, as a diagnostic of distance from a star’s surface. This is because UV emission from the star excites electrons from the upper level of one transition to the upper level of another, thus strengthening the first at the expense of the second. We modelled these line complexes in the new data from NASA’s orbiting Chandra X-ray Observatory for 𝜁 Puppis, an O supergiant star, using both a three-Gaussian and a wind line profile model. Our preliminary results indicate that the hot plasma is not very close to the photosphere, consistent with wind shock models which predict shock onset radii around 1.5𝑅∗, and inconsistent with coronal emission models. Future work will include exploring the effects of satellite line blending and UV transport through the wind.

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We use the transit method to study gas giant planets that are in very close proximity to their host stars, which are known as “hot Jupiters.” Atmospheric mass loss is likely to be significant in sculpting this population of close in planets. By observing the wavelength-dependent decrease in light when the planet passes in front of its host star, we can detect excess absorption from the escaping atmosphere. We use an ultra-narrow band filter centered on the helium (He) 1083 nm transition line to observe transits. In this line, planets’ upper atmospheres are opaque, causing an increased transit depth relative to broadband transit observations at nearby wavelengths. The transit depth in this line can be used to map the size of the region containing metastable helium and quantify the corresponding atmospheric escape rate. We observed two transits of the hot Jupiter HAT-P-18b in this line using the 200” Hale Telescope at Palomar Observatory and report the first-ever detection of outflowing gas from its upper atmosphere. This is only the seventh exoplanet with detected helium absorption, and the faintest system for which such a measurement has been made.

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I demonstrate the viability of determining atmospheric properties from spectral observations of a nearby transiting three-planet system around the K star GJ 9827. Using the open-sourced exoplanet modeling software Exo-Transmit, I created idealized transit depth distributions for each of the three planets and varied the metallicity. After accounting for the expected signal- to-noise ratio distribution, spectral resolution and wavelength range of the James Webb Space Telescope (JWST), I found even with limited observing time, near-infrared spectroscopy ob- servation using JWST could viably produce precise metallicity measurements of each planet. In addition to studying the atmosphere of the GJ 9827 system, I worked on creating an obser- vation program to search for exoplanets around bright hot stars. Analyzing the temperature and brightness distribution of stars with confirmed exoplanets demonstrates the transit and radial velocity exoplanet detection techniques have a selection bias that underrepresents hot and bright stars. The observation program I developed will use Wesleyan University’s new 24-inch telescope to search for exoplanets around hot and bright stars in order to broaden the distribution of discovered exoplanets conducive to atmospheric characterization.

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The Chandra x-ray spectral measurements of the O supergiant ζ Pup taken in 2018 and 2019 indicate a long-term variation in both stellar wind emission line flux and absorption signatures as compared to data taken in 2000. Fitting 10 strong x-ray emission lines to an asymmetric, Doppler-broadened emission line profile model that includes the effects of wind absorption, we find a 13 percent flux increase since 2000 and surprisingly a mass loss rate of 2.68 ± 0.08 × 10−6M⊙ yr−1. This represents a 50 percent increase over 18 years. Because the result is unexpected, we supplement the line profile fitting with a non-parametric analysis and also with Gaussian fitting to confirm the changes in the emission line profile properties.

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It is not clear which galaxies caused the universe to reionize over 12.5 billion years ago. The process of reionization occurred when intergalactic hydrogen became ionized by absorbing Lyman continuum (LyC) photons. It is impossible to observe LyC emissions from galaxies in the early universe. I used the Cloudy gas models to predict the gas intensity ratios of galaxies during that period with age, ionization parameter, optical depth, density and metallicity as the free parameters. I plotted the gas intensity ratios of the Cloudy models and the galaxies from The HST Low-Redshift Lyman Continuum Survey to find the physical properties of the LyC-leaking galaxies. The line ratios most sensitive to optical depth are He II(4686Å)/H-beta, Ne III(3869Å)/O II(3726+3729Å), and O III(4363Å)/O III(5007Å). The majority of the sample galaxies are closest to the lines of the higher optical depth and ionization parameter values and the 1.0 Myr models at all metallicities.

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Green Pea galaxies are considered analogues to early galaxies during the Epoch of Reion- ization (z > 6) because of their Lyman continuum (LyC) and Lyman alpha (Ly𝛼) emission. GPs then can provide information about how early galaxies re-ionized the intergalactic medium during cosmological reionization. Studying the kinematics of GPs affords us insight into the mechanisms responsible for the escape of LyC and Ly𝛼 radiation in these star-forming galaxies. Spectroscopic data of GPs provide information about said kinematics via the shape of the spectral lines. Having obtained data of GPs J1735 and J0851 using the ARC Echelle Spectrograph, I process the spectroscopic data through an IRAF data reduction pipeline and produce final spectra of J1735 and J0851 for future model fitting and analysis.

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We evaluate HI surveys as a cosmological probe of small scale structure and attempt to determine the survey criteria necessary to test ultra-light axion (ULA) dark matter models. Standard cold dark matter (CDM) models predict a large population of low-mass galactic haloes, whereas ULA models demonstrate significant suppression in this small-scale regime, with halo mass cutoffs of 10^12𝑀⊙ to 10^7𝑀⊙ corresponding to ULA masses of 10^(−24)eV to 10^(−20)eV, respectively (Marsh & Silk 2014). We conduct mock HI surveys as they would appear in CDM and a variety of ULA cosmologies to determine the detectability of these cutoffs in observational reconstructions of the HI mass function (HIMF) and corresponding halo mass function (HMF). We generate random, homogeneously populated mock universes with cosmological parameters adjusted to match CDM and ULA models. We observe the mock universes with hypothetical analogs of the mass-limited ALFALFA and WALLABY surveys (Haynes et al. 2018; Koribalski et al. 2020). The resulting statistical previews of CDM and ULA universes allow us to gauge the capabilities of these surveys through the lens of ULA cosmology.

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In the late 1990s, pioneering studies led to the discovery of a previously unknown population of galaxies known as dusty star-forming galaxies (DSFGs). These galaxies have some of the largest star-forming rates in the Universe. DSFGs were not detected in previous optical wavelength surveys designed to detect star-forming galaxies due to their dusty nature. The dust present in these DSFGs absorbs most of the ultraviolet and optical emission radiated from the surrounding stars, and re-emits the energy at far-infrared (FIR)/submillimeter wavelengths. I will be reporting on a lens model for a strongly, gravitationally-lensed DSFG first identified in the Atacama Cosmology Telescope (ACT) 470 𝑑𝑒𝑔2 equatorial field survey. The data I am presenting was obtained using the WFC3/IR F160W (∼ 𝐻) filter on the Hubble Space Telescope (HST). Our analysis relied on the use of the lensmodel (Keeton 2011) and pixsrc (Tagore Keeton 2014) software, which we used to de-lens the DSFG in order to reconstruct a pixelated model of the system. The results presented here are preliminary as we hope to use this model to help inform a complementary dataset in the submillimeter regime to finalize the lens model. Once finalized, the lens model of these data will help us better understand the physical properties of the DSFG and will help us better understand how galaxies form and evolve.

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We analyze spectroscopic observations of five young massive clusters (YMCs) in the barred spiral galaxy NGC 1313 to obtain detailed abundances from their integrated light. Our sample of YMCs was observed with the X-Shooter spectrograph on the Very Large Telescope (VLT). We make use of theoretical isochrones to generate synthetic integrated-light spectra, iterating on the individual elemental abundances until converging on the best fit to the observations.Our preliminary results give us the overall metallicities of the star clusters within NGC 1313. We observe an early trend where the metallicity of the stellar clusters decreases as their galactocentric distance increases.

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